Part 1 Structure and Function of the Respiratory System

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Part 1 Structure and Function of the Respiratory System

When you can not breath, nothing else matters

Slogan of the American Lung Association

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Respiration is the process by which the body takes in and utilizes oxygen (O2) and gets rid of carbon dioxide (CO2).

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An Overview of Key Steps in Respiration

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Respiration can be divided into four major functional events

• Ventilation: Movement of air into and out of

lungs

• Gas exchange between air in lungs and blood

• Transport of oxygen and carbon dioxide in the

blood

• Internal respiration: Gas exchange between

the blood and tissues

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Respiratory System Functions • Gas exchange: Oxygen enters blood and carbon dioxide leaves• Regulation of blood pH: Altered by changing blood carbon dio

xide levels• Voice production: Movement of air past vocal folds makes sou

nd and speech• Olfaction: Smell occurs when airborne molecules drawn into na

sal cavity• Protection: Against microorganisms by preventing entry and re

moving them• Metabolism: Synthesize and metabolize different compounds

(Nonrespiratory Function of the Lung)

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Section I ANATOMY OF THE RESPIRATORY TRACT

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Respiratory System Divisions

• Upper Airway– Nose, pharynx,

larynx and associated structures

• Lower Airway– trachea, bronchi,

lungs

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Conducting Zone

• All the structures air passes through before reaching the respiratory zone.

• Cartilage holds tube system open and smooth muscle controls tube diameter

• Warms and humidifies inspired air.

• Filters and cleans:

Insert fig. 16.5

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Respiratory Zone

• Region of gas exchange between air and blood.

• Includes respiratory bronchioles and alveolar sacs.

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Airway branching

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Section II BLOOD SUPPLY TO THE LUNG

• Two separate blood supplies: pulmonary circulation and bronchial circulation• Pulmonary circulation• Bronchial circulation

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Pulmonary circulation

• Brings deoxygenated blood from the right ventricle to the gas-exchange units

• At the gas-exchanging units, oxygen is picked up and carbon dioxide is removed from the blood

• The oxygenated blood returned to the left atrium for distribution to the rest of the body

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Bronchial circulation• Arise from the aorta

• Provides nourishments to the lung parenchyma （肺实质）

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Section III MUSCLES OF RESPIRATION • Inspiratory muscle:

• Diaphragm and Abdominal breathing （腹式呼吸）

• external intercostal muscle and thoracic breathing （胸式呼吸）

• accessory muscle of inspiration

• Expiratory muscle• relax during normal breathing

• Internal intercostal muscle

• Muscles of the abdominal wall

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Thoracic Walls and Muscles of Respiration

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Breathing Rate

• At rest: 10-20 breaths / minute

• During exercise: 40 - 45 at maximum exercise in adults

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Thoracic Volume

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Mechanisms of Breathing: Mechanisms of Breathing: How do we change the volume of the rib cage ?How do we change the volume of the rib cage ?

To Inhale is an ACTIVE processTo Inhale is an ACTIVE process• DiaphragmDiaphragm

Rib CageRib Cage

ContractContract

DiaphragmDiaphragmVolumeVolume

•External Intercostal Muscles External Intercostal Muscles

IntercostalsIntercostalsContractContract

to Liftto LiftRibRib

SpineSpine

RibsRibs VolumeVolume

Both actions occur simultaneously – otherwise not effectiveBoth actions occur simultaneously – otherwise not effective

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Pleura

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•Pleural fluid produced by pleural membranes

–Acts as lubricant

–Helps hold parietal and visceral pleural membranes together

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Ventilation

• Movement of air into and out of lungs

• Air moves from area of higher pressure to

area of lower pressure

• Pressure is inversely related to volume

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Alveolar Pressure Alveolar Pressure Changes During Changes During RespirationRespiration

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Chest WallChest Wall(muscle, ribs)(muscle, ribs)

Principles of BreathingPrinciples of BreathingFunctional Unit: Chest Wall and Lung Functional Unit: Chest Wall and Lung

ConductingConductingAirwaysAirways

DiaphragmDiaphragm(muscle)(muscle)

LungsLungsGas ExchangeGas Exchange

Follows Boyle’s Law:Follows Boyle’s Law:Pressure (P) x Volume (V) = ConstantPressure (P) x Volume (V) = Constant

Pleural CavityPleural CavityImaginary Space betweenImaginary Space betweenLungs and chest wallLungs and chest wall

Pleural CavityPleural CavityVery small space Very small space Maintained at negative pressureMaintained at negative pressureTransmits pressure changes Transmits pressure changes Allows lung and ribs to slideAllows lung and ribs to slide

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CWCW

Follows Boyle’s Law: PV= CFollows Boyle’s Law: PV= C

At Rest with mouth open PAt Rest with mouth open Pbb = P = Pi i = 0= 0

DD

PPii

AA

PSPS

PPbb

Airway OpenAirway Open

Principle of BreathingPrinciple of Breathing

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CWCW


At Rest with mouth open PAt Rest with mouth open Pbb = P = Pi i = 0= 0Inhalation: Inhalation: - Increase Volume of Rib cageIncrease Volume of Rib cage- Decrease the pleural cavity pressureDecrease the pleural cavity pressure- Decrease in Pressure inside (P- Decrease in Pressure inside (Pii) lun) lungsgs

DD

PPii

AA

PSPS

PPbb



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CWCW


At Rest with mouth open PAt Rest with mouth open Pbb = P = Pii = 0 = 0Inhalation: Inhalation:

- PPbb outside is now greater than P outside is now greater than Pii

- Air flows down pressure gradient- Air flows down pressure gradient- Until Pi = PbUntil Pi = Pb

DD

PPii

AA

PSPS

PPbb



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CWCW


DD

PPii

AA

PSPS

PPbb


At Rest with mouth open PAt Rest with mouth open Pbb = P = Pii = 0 = 0

Exhalation: Opposite ProcessExhalation: Opposite Process- Decrease Rib Cage VolumeDecrease Rib Cage Volume


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CWCW



Exhalation: Opposite ProcessExhalation: Opposite Process- Decrease Rib Cage VolumeDecrease Rib Cage Volume- Increase in pleuralIncrease in pleural

cavity pressure cavity pressure - Increase P - Increase Pii

DD

PPii

AA

PSPS

PPbb



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CWCW



Exhalation: Opposite ProcessExhalation: Opposite Process- Decrease Rib Cage VolumeDecrease Rib Cage Volume- Increase PIncrease Pii

- Pi is greater than PPi is greater than Pbb

- Air flows down pressure gradientAir flows down pressure gradient- Until PUntil Pii = P = Pbb again again

DD

PPii

AA

PSPS

PPbb



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Section IV SURFACTANT AND SURFACE TENSION

• Surface tension ( 表面张力） : a measure of the attraction force of the surface molecules per unit length of the material to which they are attached

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Surface Tension

• Force exerted by fluid in alveoli to resist

distension• Lungs secrete and absorb fluid, leaving a

very thin film of fluid.

• H20 molecules at the surface are attracted

to other H20 molecules by attractive forces.

– Force is directed inward, raising pressure in

alveoli.

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What is Surface What is Surface Tension ?Tension ?

Within Fluid Within Fluid All forces balanceAll forces balance

At surfaceAt surfaceUnbalanced forces Unbalanced forces Generate TensionGenerate Tension

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Surface Tension

• Law of Laplace:– Pressure in alveoli

–directly proportional to surface tension

–inversely proportional to radius of alveoli

– if surface tension were the same in all alveolus....

Insert fig. 16.11

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CollapseCollapse

ExpandExpand

Effect of Surface Tension on Alveoli sizeEffect of Surface Tension on Alveoli size

AirAir FlowFlow

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Surfactant ( 表面活性物质）• Phospholipid produced

by alveolar type II cells.

• Lowers surface tension.

– Reduces attractive

forces of hydrogen

bonding

– by becoming

interspersed between

H20 molecules.

• Surface tension in

alveoli is

reduced.

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Area dependence of Surfactant actionArea dependence of Surfactant action

TensionTension

AreaAreaSurfactantSurfactant

Increase AreaSalineSaline

Slider - Change Surface AreaSlider - Change Surface Area

SalineSaline

DecreaseArea

Low S/unit Area

High S/unit Area

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Surfactant prevents alveolar collapse

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Volume LVolume L

RVRVPleural PressurePleural Pressure00

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00 - 30 cm H- 30 cm H22OO- 15- 15

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Normal (with surfactant)Normal (with surfactant)Saline FilledSaline Filled

Without surfactant

Volume-pressure curves of lungs filled with saline and with air (with or without surfactant)

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Physiology Importance of Surfactant

• Reduce the work of breathing• Stabilize alveoli

• Prevent collapse and sticking of alveoli

• Maintain the dryness of the alveoli• Prevent the edema of the alveoli

Documents

Part 1 Structure and Function of the Respiratory System